1. Field of the Invention
The present invention relates to a technique for a light-emitting device, which includes a light-emitting element and an electrostatic protection element for protecting the light-emitting element from electrostatic breakdown, as well as for a vehicle lamp including use of the light-emitting device. The technique enables reliable detection of a nonillumination state of the light-emitting device.
2. Background Art
In a light-emitting device employed as a light source of a lamp, an electrostatic protection element, such as a Zener diode or a capacitor, is disposed in parallel with a light-emitting chip of the light-emitting device as a measure against static electricity of the light-emitting chip. For instance, known configurations of a white light-emitting diode (LED) employing a nitride semiconductor material, or the like, for its LED chip, include that in which a Zener diode is connected in parallel with the LED chip, thereby packaging the Zener diode and the LED chip into a single package so as to prevent electrostatic breakdown of the element. More specifically, the Zener diode and the LED chip are disposed in a single package in a state where a cathode of the LED chip and an anode of the Zener diode are connected together, and an anode of the LED chip and a cathode of the Zener diode are connected together.
Electric connection between the LED chip and the Zener diode is established through bonding with use of gold wire having the same diameter.
In a configuration in which a plurality of light-emitting devices (or light-emitting modules), each device including a light-emitting element and an electrostatic protection element, are connected in parallel to thus serve as a light source, a lapse of even any one of the light-emitting elements into an illumination-disabled state problematically affects optical performance (degradation in light distribution performance, or the like, in the case of application to a light source for a vehicle). Therefore, nonillumination detection of the respective light-emitting devices is required. For instance, the following nonillumination detection method is applied to a configuration in which all the light-emitting elements are connected in series, and the light-emitting elements are driven through its constant current control.
(I) A method of monitoring current values of a light-emitting device group; and
(II) a method of monitoring voltage values across the respective light-emitting devices.
In these cases, since a generally assumed failure is that of the light-emitting element in an open-circuit mode, detection of a failure in a short-circuit mode may fail (that is, during a short-circuit mode of a light-emitting element or an electrostatic protection element, a nonillumination state may fail to be detected). Accordingly, possibility of occurrence of a nonillumination state of a light-emitting device resulting from a failure in a short-circuit mode must be minimized.